There’s some microdegradation of DNA after only a few days. Microdegradation means DNA, or the proteins that support its structure, start to break down during the freezing process.
How significant this is depends on the circumstances.
When sperm are frozen, there are generally millions to spare. You can be confident that there will be viable sperm when a sample thaws. Sometimes the sperm lose the capacity to enter eggs on their own, but this can be treated through IVF with ICSI. If sperm counts are good going into the freezer, we generally expect them to be good coming out – even years later!
Meanwhile, a single egg taken for pre-implantation genetic screening can start to break down very quickly, even after only a week.
So what about the embryos themselves? We’ve found that embryo quality does not change over hours, days or weeks. But it can over several years.
It’s also worth a reminder that, in my experience, frozen-embryo transfer are not as successful as a fresh ones. There’s a lot of conflicting information on this subject, though. Some groups claim significantly higher success rates with frozen-embryo transfer versus fresh. In many labs, however, freezing truly does compromise embryos when they thaw, and can have significantly lower success rates.
As the technology advances, we hope to see substantially better frozen-embryo transfer success rates in late 2014 and beyond.